Sheet feeding device and image forming apparatus

ABSTRACT

A boundary is formed between a separating pad holding member and a separating pad in a sheet conveyance direction such that a sheet feeding device includes: a feeding roller having a feeding roller surface at a part in a rotational direction; the separating pad which separates the sheet at a holding portion between the feeding roller surface and the same; the separating pad holding member which presses the separating pad against the feeding roller; and a rolling member which is disposed coaxially with the feeding roller and abuts against the separating pad free from the holding state in cooperation with the roller surface; the feeding roller surface abutting against the separating pad holding member and the separating pad in this order, respectively, via the sheet S during the rotation of the feeding roller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device which separatessheets such as originals or recording sheets one by one and feeds them,and an image forming apparatus having the sheet feeding device such as acopying machine, a facsimile or a printer.

2. Description of the Related Art

In an image forming apparatus such as a copying machine or a printer,the stability of feeding performance and the reduction of an operationalnoise has been required for a sheet feeding device which separatessheets such as originals or recording sheets one by one and feeds them.There has been conventionally known a sheet feeding device having asystem in which sheets are separated one by one by a semicircularfeeding roller and a separating pad pressed against the feeding roller.In the sheet feeding device of the separation system, vibrations may begenerated between the feeding roller and the separating pad according toa type of sheet to be fed, and further, the vibrations may cause anabnormal noise (i.e., a chattering noise).

In view of this, there has been proposed a technique which provides avibration suppressing member for a separating pad so as to prevent anyvibration of the separating pad, thereby preventing any generation of anabnormal noise, as disclosed in Japanese Patent Application Laid-openNo. 8-91608. This configuration can produce an effect of suppressing thevibration of the separating pad, generated due to a slide-contact of asheet to be fed at a predetermined speed with the separating pad.

However, even the above-described prior art cannot prevent any vibrationcaused by friction between the sheet and the separating pad generated atthe time of the abutment of the feeding roller rotated during the sheetfeeding against the separating pad via the sheet, and therefore, thevibration causes an abnormal noise (i.e., a chattering noise).

In order to suppress any generation of the abnormal noise, it is devisedthat a pressing force of the separating pad against the feeding rolleris reduced or a friction coefficient of the separating pad is reduced.However, this degrades the separability of the sheet by the separatingpad, thereby achieving a satisfactory separating/feeding performance.

Moreover, with a configuration in which a collision is alleviated duringthe abutment of the feeding roller against the separating pad, it isdevised that the rotational speed of the feeding roller is reduced downto a speed enough to prevent any generation of the abnormal noise.However, this reduces a sheet conveyance speed.

SUMMARY OF THE INVENTION

The present invention suppresses any vibration generated during anabutment of a feeding roller against a separating pad without anyreduction of a sheet conveyance speed or any degradation of aseparating/feeding performance, so as to prevent any generation of anabnormal noise (i.e., a chattering noise) due to the vibration.

According to a typical aspect of the present invention, a sheet feedingdevice includes: a feeding roller having a roller surface, on which asheet is fed, at a part in a rotational direction; a separating padwhich is disposed opposite to the feeding roller and the sheets areseparated between the separating pad and the roller surface; aseparating pad holding member which holds the separating pad therein andpresses the separating pad against the feeding roller; and a rollingmember which abuts against the separating pad free from the abuttingstate with the roller surface; wherein the roller surface abuts againstthe separating pad holding member and the separating pad in this ordervia the sheet during the rotation of the feeding roller.

According to the present invention, the vibration generated during theabutment of the feeding roller against the separating pad can besuppressed without any reduction of the sheet conveyance speed or anydegradation of the separating/feeding performance, so that thegeneration of an abnormal noise (i.e., a chattering noise) due to thevibration can be prevented.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating theconfiguration of an image forming apparatus provided with a sheetfeeding device;

FIG. 2 is a perspective view illustrating essential parts of the sheetfeeding device;

FIG. 3 is a cross-sectional view illustrating a standby state before asheet separating/feeding operation by the sheet feeding device;

FIG. 4 is a cross-sectional view illustrating a state during sheetseparation/feeding by the sheet feeding device;

FIG. 5 is a cross-sectional view illustrating a state during sheetseparation/conveyance by the sheet feeding device;

FIG. 6 is a cross-sectional view illustrating the state of the sheetfeeding device during the sheet conveyance;

FIGS. 7A and 7B are views illustrating the configuration of a separatingpad in the sheet feeding device in a first exemplary embodiment;

FIG. 8 is a cross-sectional view illustrating, in enlargement, a sheetfeeding operation by the sheet feeding device;

FIG. 9 is another cross-sectional view illustrating, in enlargement, thesheet feeding operation by the sheet feeding device;

FIGS. 10A and 10B are views illustrating the configuration of aseparating pad in a sheet feeding device in a second exemplaryembodiment;

FIGS. 11A and 11B are views illustrating the configuration of aseparating pad in a sheet feeding device in a third exemplaryembodiment; and

FIGS. 12A and 12B are views illustrating the configuration of aseparating pad in a sheet feeding device in a fourth exemplaryembodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments according to the present inventionwill be illustratively described in detail in reference to the attacheddrawings. Here, dimensions, materials and shapes of component parts andtheir relative arrangement described in the exemplary embodiments belowshall be appropriately varied according to configurations or variousconditions of an apparatus, to which the present invention is applied.As a consequence, the scope of the present invention is not limited toonly those, unless specified otherwise.

First Exemplary Embodiment

FIG. 1 is a view exemplifying the schematic configuration of an imageforming apparatus provided with a sheet feeding device, and FIG. 2 is aperspective view illustrating essential parts of the sheet feedingdevice.

As shown in FIGS. 1 and 2, an inside plate 101 is disposed in a sheetcassette 114, and thus, presses upward sheets S stacked thereon by forceof an urging spring 113. A feeding roller 102 is fixed to a supportshaft 108, to be rotatably supported thereon. An uppermost sheet out ofthe sheets S pressed up by the inside plate 101 abuts at the tip thereofagainst the feeding roller 102. The feeding roller 102 has a rollersurface 102 r which feeds the sheet thereon. The roller surface 102 r isformed into an arcuate shape in cross section, and is disposed at a partof the feeding roller in a rotational direction. Here, the feedingroller 102 has the roller surface 102 r formed into a semicircle incross section. A front portion 102 ra illustrated in FIG. 8 of theroller surface 102 r in the rotational direction is formed into asmoothly arcuate shape in such a manner that a radius from the axis ofthe support shaft 108 becomes gradually smaller.

Circular abutment rollers (i.e., rolling members) 109 are rotatablydisposed in the support shaft 108 having the feeding roller 102 fixedthereto on both sides of the feeding roller 102 in a sheet widthwisedirection perpendicular to a sheet conveyance direction. In other words,the abutment rollers 109 are rotatably disposed coaxially with thefeeding roller 102.

A separating pad 104 faces the feeding roller 102, and separates thesheets one by one at a holding portion between the roller surface 102 rand the same. A separating pad holding member 103 holds the separatingpad 104 therein, and further, presses the separating pad 104 against thefeeding roller 102. The separating pad holding member 103 is disposedunder the feeding roller 102 in an oscillatable manner within apredetermined range on a hinge h. The separating pad 104 is disposed atan upper portion of the separating pad holding member 103, and further,abuts against a lower portion of the feeding roller 102. A spring 105urges the separating pad holding member 103 toward the feeding roller102. A conveying guide 106 serves as a conveyance path for the sheet Sconveyed by the feeding roller 102. Conveying rollers 107 convey thesheet S to a next process.

The conveyed sheet S is further conveyed by a transfer belt 115, issubjected to transfer of a toner image from each of photosensitive drums110K, 110C, 110M and 110Y and to fixture by a heat fixing unit 111, andthereafter, is discharged onto a discharge tray 112.

A radius Ra of the roller surface 102 r of the feeding roller 102 isgreater than a radius Rb of the abutment roller 109 (Ra>Rb). Therefore,when the abutment roller 109 is fixed to the support shaft 108, theperipheral surface of the abutment roller 109 is located inside of theroller surface 102 r. As a consequence, the abutment roller 109 does notabut against the separating pad 104 in a holding state of the rollersurface 102 r of the feeding roller 102 and the separating pad 104: incontrast, the abutment roller 109 abuts against the separating pad 104which is released from the holding state in cooperation with the rollersurface 102 r of the feeding roller 102.

FIG. 3 is a cross-sectional view schematically illustrating a standbystate before the sheet is separated and fed. The inside plate 101 havingthe sheets S stacked thereon is lifted upward by the urging spring 113,as illustrated in FIG. 1. In this manner, the inside plate 101 comes toa halt in the state in which the tip of the uppermost sheet out of thesheets S abuts against the abutment rollers 109, and then, the sheet canbe turned to a freely fed state. Moreover, the separating pad 104 is inan abutment state against the abutment rollers 109 by the energizationof the spring 105. That is to say, the position of the separating pad104 in the standby state depends upon the abutment roller 109.

FIG. 4 is a cross-sectional view schematically illustrating a stateduring sheet separation/feeding. Upon start of a sheet feedingoperation, the rotation of the feeding roller 102 enables the rollersurface 102 r of the feeding roller 102 to abut against the uppermostsheet S, which is then fed, as illustrated in FIG. 4. The fed sheet S isconveyed to between the conveying rollers 107 through a nip unit servingas a holding unit defined between the feeding roller surface 102 r andthe separating pad 104.

Here, the sheet S held between the feeding roller surface 102 r and theseparating pad 104 is pressed against the separating pad 104 by thefeeding roller 102. An interrelationship among a friction μ1 between theseparating pad 104 and the sheet, a friction μ2 between the sheets, anda friction μ3 between the sheet and the feeding roller 102 isestablished in such a manner as to meet an inequality of μ2<μ1<μ3. Thus,even if the plurality of sheets S are fed by the feeding roller 102 atthe same time, the sheets can be separated from each other, and then,are fed one by one.

The feeding roller 102 is rotated once by a clutch mechanism, notillustrated. At this time, the tip of the sheet S is conveyed up tobetween the conveying rollers 107, as illustrated in FIG. 5. Thereafter,the feeding roller 102 is stopped such that portions, at which theroller surface 102 r of the feeding roller 102 is cut out, that is, theabutment rollers 109 face the separating pad 104, as illustrated in FIG.6.

At this time, the conveying rollers 107 continue conveying the sheet S.Therefore, the sheet S passing between the abutment rollers 109 and theseparating pad 104 is conveyed by the conveying rollers 107 whileremaining held between the abutment rollers 109 and the separating pad104. Here, the abutment rollers 109 are not fixed to the support shaft108, and thus, are rotated together with the sheet S to be conveyed. Theabutment rollers 109 are rotated in this manner, and further, the sheetS is conveyed in contact with the separating pad 104. Consequently, thedual feeding of the sheets S can be prevented with a small back tensionagainst a conveyance force.

As illustrated in FIG. 4, the feeding roller 102 abuts against theseparating pad 104 via the sheet S during the sheet separatingoperation. At this time, the separating pad holding member 103 ispressed by the feeding roller 102, to be turned on the hinge h.Therefore, the feeding roller 102 abruptly receives a reaction from thespring 105 of the separating pad holding member 103, and further, thesheet S and the separating pad 104 strongly slide each other at theabutment portion against the feeding roller surface 102 r. In this way,a stick-slip (i.e., a frictional vibration phenomenon) occurs betweenthe sheet S and the separating pad 104 according to the type of sheet Sor an environmental ambient (such as a temperature or a humidity),thereby raising an undesired possibility of generation of an abnormalnoise due to the stick-slip (hereinafter referred to as “a strange noiseof a pad”). The stick-slip signifies a phenomenon in which objectsrepeatedly slide on or interfere with a given surface by frictiontherebetween when the objects take a sliding motion, thereby inducing africtional vibration.

Although the generation of the strange noise of the pad may besuppressed by reducing a spring pressure of the spring 105 which pressesthe separating pad holding member 103, it is difficult to suppress thegeneration of the strange noise of the pad since the dual feeding occursdue to the unsatisfactory separation of the sheets S from each otheraccording to the type of sheet S. Otherwise, it may be construed thatthe strange noise of the pad is prevented by varying the frictioncoefficients of the feeding roller 102 and the separating pad 104, butit is difficult to find a combination of materials capable of copingwith the type of sheet S, an environmental change and the like.

In view of this, a boundary between the separating pad holding member103 and the separating pad 104 in a sheet conveyance direction is set insuch a manner that the feeding roller surface 102 r abuts against theseparating pad holding member 103 and the separating pad 104 in thisorder via the sheet S, respectively, during the rotation of the feedingroller 102. This will be described in detail in reference to FIGS. 7 to9.

A boundary 103 b between the separating pad holding member 103 and theseparating pad 104 is illustrated in FIGS. 7A and 7B. The front portion102 ra of the feeding roller surface 102 r first abuts against thevicinity of the boundary 103 b of the separating pad holding member 103during one rotation of the feeding roller 102, as illustrated in FIG. 8(hereinafter referred to as “a point A1”). Next, the peripheral surfaceof the roller surface 102 r abuts against the separating pad 104 via thesheet S, as illustrated in FIG. 9 (hereinafter referred to as “a pointA2”). In this manner, the boundary 103 b is defined between theseparating pad holding member 103 and the separating pad 104. When thesheet S reaches the point A2, the separating pad holding member 103 andthe feeding roller surface 102 r are separated from each other.

Specifically, it is designed such that the roller surface 102 r of thefeeding roller 102 abuts against the separating pad holding member 103at the point A1 before the abutment against the separating pad 104 atthe point A2 via the sheet S. Since the separating pad holding member103 is made of a resin material (here, PPE and PS), the frictioncoefficient of the surface is smaller than that of the separating pad104. Therefore, upon the abutment of the feeding roller 102 via thesheet S, the separating pad holding member 103 and the sheet S slideeach other, so that no stick-slip occurs between the feeding roller 102and the sheet S, thereby preventing any occurrence of the strange noiseof the pad. At this time, the separating pad holding member 103 has beenalready maintained substantially at an angle, at which the sheetseparating operation is performed, owing to the previous abutmentagainst the feeding roller 102. As a consequence, when the separatingpad 104 and the feeding roller 102 next abut against each other via thesheet S, they can abut against each other without any great change inangle. Thus, the separating pad 104 and the sheet S cannot stronglyslide each other at the time of the abutment against the feeding roller102, thereby preventing any occurrence of the strange noise of the pad.

Incidentally, in the case where the boundary 103 b between theseparating pad holding member 103 and the separating pad 104 is formedexcessively downstream of the above-setting position in the sheetconveyance direction, as follows: the feeding roller surface 102 rremains abutting against the separating pad holding member 103 evenafter the front portion 102 ra abuts against the separating pad holdingmember 103, and therefore, cannot satisfactorily abut against theseparating pad 104 via the sheet, thereby inducing the dual feeding ofthe sheet. In contrast, in the case where the boundary 103 b between theseparating pad holding member 103 and the separating pad 104 is formedupstream of the above-set position in the sheet conveyance direction,the feeding roller surface 102 r cannot abut against the separating padholding member 103 via the sheet, resulting in the occurrence of thestrange noise of the pad, like in the prior art. Alternatively, in thecase where the boundary 103 b is formed more upstream, the tip of thefed sheet S intrudes while forming an obtuse angle with respect to theseparating pad 104, and therefore, the sheet S is liable to bedeficiently conveyed due to its interference.

As described above, in the present exemplary embodiment, the boundary103 b between the separating pad holding member 103 and the separatingpad 104 is set in such a manner that the feeding roller surface 102 rabuts against the separating pad holding member 103 and the separatingpad 104 in this order via the sheet S, respectively. As a result, thevibration generated during the abutment of the feeding roller 102against the separating pad 104 via the sheet can be suppressed withoutany reduction of the sheet conveyance speed or any degradation of theseparating/feeding performance, thus preventing any generation of theabnormal noise (i.e., a chattering noise) due to the vibration.

Second Exemplary Embodiment

A sheet feeding device in a second exemplary embodiment is described inreference to FIGS. 10A and 10B. Here, a mechanical structure in thepresent exemplary embodiment is substantially identical to that in thefirst exemplary embodiment. Therefore, reference numerals illustrated inFIGS. 1 to 9 are used, and further, constituent elements designated bythe reference numerals will not be described. In addition, an operationin the second exemplary embodiment also is identical to that in thefirst exemplary embodiment, and therefore, its description will beomitted below.

In the present exemplary embodiment, out of boundaries 103 b between aseparating pad holding member 103 and a separating pad 104, boundaries103 b 2 in a second region are formed in a sheet conveyance directionupstream of another boundary 103 b 1 in a first region, against which afeeding roller surface 102 r abuts. Here, a distance t between theboundary 103 b 1 and the boundary 103 b 2 is set to 0.8 mm, although atip of a fed sheet S interferes with the separating pad 104, to beliable to be deficiently conveyed when the boundaries 103 b 2 are formedmore upstream in the sheet conveyance direction (here, the distance t isgreater than 2 mm).

The second regions in the separating pad holding member 103 are formedon both sides of the first region (having a width 103 w) in a sheetwidthwise direction. Moreover, the width of the boundary 103 b 1 of thefirst region (having the width 103 w) is set to be narrower than adistance between abutment rollers 109. Here, the width 103 w of thefirst region is set to be equal to a length of the feeding rollersurface 102 r in the sheet widthwise direction.

A front portion 102 ra in the feeding roller surface 102 r first abutsagainst the vicinity of the boundary 103 b 1 of the separating padholding member 103 during one rotation of the feeding roller 102, asillustrated in FIG. 8 (hereinafter referred to as “a point A1”). Next,the peripheral surface of the feeding roller surface 102 r abuts againstthe separating pad 104 via the sheet S, as illustrated in FIG. 9(hereinafter referred to as “a point A2”). In this manner, the boundary103 b 1 is formed between the separating pad holding member 103 and theseparating pad 104. When the sheet S reaches the point A2, theseparating pad holding member 103 and the feeding roller surface 102 rare separated from each other.

Additionally, as illustrated in FIGS. 10A and 10B, out of the boundaries103 b between the separating pad holding member 103 and the separatingpad 104, only the boundary 103 b 1 formed at the center projects in thesheet conveyance direction in comparison with the boundaries 103 b 2formed on both sides in the sheet widthwise direction. As a consequence,the tip of the sheet S abuts against the separating pad 104 earlier thanthe boundary 103 b 1 within a range of the boundaries 103 b 2 at bothends of the separating pad 104. Therefore, in the case of dual feedingof sheets, a function of preventing any dual feeding is inhibited frombeing degraded by a sheet separating effect of mutually loosening thesheets S. Incidentally, since the feeding roller surface 102 r does notface the regions of the boundaries 103 b 2, even if the tip of the sheetS first abuts against the separating pad 104 prior to abutment againstthe vicinity of the boundary 103 b 1 of the separating pad holdingmember 103, no abnormal noise can occur due to a vibration.

Third Exemplary Embodiment

A sheet feeding device in a third exemplary embodiment is described inreference to FIGS. 11A and 11B. Here, a mechanical structure in thepresent exemplary embodiment is substantially identical to those in thefirst and second exemplary embodiments. Therefore, reference numeralsillustrated in FIGS. 1 to 9 are used, and further, constituent elementsdesignated by the reference numerals will not be described. In addition,an operation in the third exemplary embodiment also is identical tothose in the first and second exemplary embodiments, and therefore, itsdescription will be omitted below.

In the present exemplary embodiment, a separating pad holding member 103holds a sliding member 103 s, which is made of a material harder thanthe separating pad holding member 103 and has a high surfaceperformance, in a region (having a width 103 w), against which a feedingroller surface 102 r abuts, and upstream in a sheet conveyance directionof a separating pad 104. Here, an SUS plate is used as the slidingmember 103 s. In this manner, a boundary between the sliding member 103s and the separating pad 104 in the sheet conveyance direction is set insuch a manner that the feeding roller surface 102 r abuts against thesliding member 103 s and the separating pad 104 in this order via asheet, respectively, during rotation of a feeding roller 102.

Moreover, out of boundaries 103 b between the separating pad holdingmember 103 and the separating pad 104 in the sheet conveyance direction,boundaries 103 b 2 between the separating pad holding member 103 and theseparating pad 104 are formed upstream of another boundary 103 b 1between the sliding member 103 s and the separating pad 104 in the sheetconveyance direction.

Furthermore, the boundaries 103 b 2 between the separating pad holdingmember 103 and the separating pad 104 in a sheet widthwise direction areformed on both sides of the boundary 103 b 1 between the sliding member103 s and the separating pad 104. Additionally, the width (the width 103w) of the boundary 103 b 1 of the sliding member 103 s is set to benarrower than a distance between abutment rollers 109.

In the case where the separating pad holding member 103 is made of asoft material (e.g., a resin such as ABS), the separating pad holdingmember 103 may be cut off by a tip of a sheet S when the feeding roller102 repeatedly abuts against the separating pad holding member 103 viathe sheet S. Otherwise, in the case where the separating pad holdingmember 103 is made of a material having a poor surface performance(e.g., a resin material containing a large quantity of glass), the poorsurface performance may raise a fear of occurrence of deficientconveyance, for example, an interference of the tip of the sheet S withthe separating pad holding member 103. In view of this, the use of thesliding member 103 s (i.e., the SUS plate), like in the presentexemplary embodiment, enables the sheet to be stably conveyed.

A front portion 102 ra first abuts against the vicinity of the boundary103 b 1 of the sliding member 103 s via the sheet during one rotation ofthe feeding roller 102. Next, the peripheral surface of the feedingroller surface 102 r abuts against the separating pad 104 via the sheet.Therefore, during the slide between the feeding roller 102 and thesliding member 103 s via the sheet, the sheet and the sliding member 103s slide each other, so that no stick-slip occurs between the feedingroller 102 and the sheet. As a consequence, the occurrence of thestrange noise of the pad can be prevented more than in theabove-described exemplary embodiments.

Incidentally, the sliding member 103 s may be made of other materialshaving a small surface friction coefficient, thus suppressing thestrange noise of the pad in the same manner.

Fourth Exemplary Embodiment

A sheet feeding device in a fourth exemplary embodiment is described inreference to FIGS. 12A and 12B. Here, a mechanical structure in thepresent exemplary embodiment is substantially identical to those in thefirst, second and third exemplary embodiments. Therefore, referencenumerals illustrated in FIGS. 1 to 9 are used, and further, constituentelements designated by the reference numerals will not be described. Inaddition, an operation in the fourth exemplary embodiment also isidentical to those in the first, second and third exemplary embodiments,and therefore, its description will be omitted below.

In the present exemplary embodiment, a separating pad holding member 103holds a sliding member 103 e having a friction coefficient smaller thanthat of the separating pad 104 in a region (having a width 103 w),against which a feeding roller surface 102 r abuts, and upstream of aseparating pad 104 in a sheet conveyance direction. Here, an urethane-or rubber-based elastomer member is used as the sliding member 103 e. Inaddition, the friction coefficient of the separating pad 104 is 0.9 to0.8 whereas the friction coefficient of the sliding member (i.e., theelastomer member) 103 e is 0.6 to 0.5. In this manner, a boundarybetween the sliding member 103 e and the separating pad 104 in a sheetconveyance direction is set in such a manner that the feeding rollersurface 102 r abuts against the sliding member 103 e and the separatingpad 104 in this order via a sheet, respectively, during rotation of afeeding roller 102.

Moreover, out of boundaries 103 b between the separating pad holdingmember 103 and the separating pad 104 in the sheet conveyance direction,boundaries 103 b 2 between the separating pad holding member 103 and theseparating pad 104 are formed upstream of another boundary 103 b 1between the sliding member 103 e and the separating pad 104 in the sheetconveyance direction.

Furthermore, the boundaries 103 b 2 between the separating pad holdingmember 103 and the separating pad 104 in a sheet widthwise direction areformed on both sides of the boundary 103 b 1 between the sliding member103 e and the separating pad 104. Additionally, the width (the width 103w) of the boundary 103 b 1 of the sliding member 103 e is set to benarrower than a distance between abutment rollers 109.

A front portion 102 ra first abuts against the vicinity of the boundary103 b 1 of the sliding member 103 e via the sheet during one rotation ofthe feeding roller 102. Next, the peripheral surface of the rollersurface 102 r abuts against the separating pad 104 via the sheet.Therefore, also during the slide between the feeding roller 102 and thesliding member 103 e via the sheet, the sheet and the sliding member 103e slide each other, so that no stick-slip occurs between the feedingroller 102 and the sheet. As a consequence, the occurrence of a strangenoise of the pad can be prevented more than in the above-described firstand second exemplary embodiments.

Additionally, the sliding member 103 e has the frictional coefficientsmaller than those of the feeding roller 102 and the separating pad 104,thereby not only preventing any strange noise of the pad but alsoseparating sheets one by one even when a plurality of sheets dually fedslide each other between the feeding roller 102 and the sliding member103 e. Alternatively, the sliding member 103 e can assist the separationby the separating pad 104, thus preventing any deficiency of dualfeeding.

Other Exemplary Embodiments

In the above-described exemplary embodiments, a printer has exemplifiedthe image forming apparatus, but the present invention is not limited tothis. For example, the present invention may be applied to other imageforming apparatuses such as a copying machine and a facsimile, a furtherimage forming apparatus for a composite machine having a combination offunctions of a copying machine and a facsimile, or an image readingapparatus such as a scanner. The similar effects can be produced byapplying the present invention to the sheet feeding device for use inthe aforementioned image forming apparatus or image reading apparatus.

Although the sheet feeding device integrally provided in the imageforming apparatus has been illustrated in the above-described exemplaryembodiments, the present invention is not limited to this. For example,the present invention may be applicable to a sheet feeding device whichis detachably attached to an image forming apparatus. The similareffects can be produced by applying the present invention to the sheetfeeding device.

In addition, although the sheet feeding device which feeds the sheetsone by one to a recording unit which records an image on a sheet such asa recording sheet to be recorded has been illustrated in theabove-described exemplary embodiments, the present invention is notlimited to this. For example, the similar effects can be produced byapplying the present invention to the sheet feeding device which feedsthe sheets one by one to a reading unit which reads an image on a sheetsuch as an original to be read.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-159683, filed Jun. 18, 2007, which is hereby incorporated byreference herein in its entirety.

1. A sheet feeding device comprising: a feeding roller having a rollersurface, on which a sheet is fed, at a part in a rotational direction; aseparating pad which is disposed opposite to the feeding roller and thesheets are separated between the separating pad and the roller surface;a separating pad holding member which holds the separating pad thereinand presses the separating pad against the feeding roller; and a rollingmember which abuts against the separating pad free from the abuttingstate with the roller surface; wherein the roller surface abuts againstthe separating pad holding member and the separating pad in this ordervia the sheet during the rotation of the feeding roller.
 2. The sheetfeeding device according to claim 1, wherein a friction coefficient ofthe surface of the separating pad holding member is smaller than that ofthe surface of the separating pad.
 3. The sheet feeding device accordingto claim 1, wherein first and second regions, against which the rollersurface of the feeding roller abuts, are set, and further, out of theboundary between the separating pad holding member and the separatingpad, a boundary of the second region is formed more upstream in a sheetconveyance direction than a boundary of the first region.
 4. The sheetfeeding device according to claim 3, wherein the rolling members aredisposed on both sides at the roller surface of the feeding roller in asheet widthwise direction perpendicular to the sheet conveyancedirection, and further, the second regions of the separating pad holdingmember are disposed on both sides of the first region whose boundary hasa width smaller than a distance between the rolling members.
 5. A sheetfeeding device comprising: a feeding roller having a roller surface, onwhich a sheet is fed, at a part in a rotational direction; a separatingpad which is disposed opposite to the feeding roller and the sheets areseparated between the separating pad and the roller surface; aseparating pad holding member which holds the separating pad therein andpresses the separating pad against the feeding roller; and a rollingmember which abuts against the separating pad free from the abuttingstate with the roller surface; wherein the separating pad holding memberholds a sliding member, which is made of a material harder than theseparating pad holding member, in a region, against which the rollersurface abuts, and upstream of the separating pad in a sheet conveyancedirection, and the roller surface abuts against the sliding member andthe separating pad in this order via the sheet during the rotation ofthe feeding roller.
 6. The sheet feeding device according to claim 5,wherein a boundary between the separating pad and the separating padholding member is formed more upstream in a sheet conveyance directionthan a boundary between the separating pad and the sliding member,against which the roller surface of the feeding roller abuts.
 7. Thesheet feeding device according to claim 6, wherein the rolling membersare disposed on both sides at the roller surface of the feeding rollerin a sheet widthwise direction perpendicular to the sheet conveyancedirection, and further, the boundaries between the separating pad andthe separating pad holding member are formed on both sides of theboundary between the separating pad and the sliding member whoseboundary has a width smaller than a distance between the rollingmembers.
 8. A sheet feeding device comprising: a feeding roller having aroller surface, on which a sheet is fed, at a part in a rotationaldirection; a separating pad which is disposed opposite to the feedingroller and the sheets are separated between the separating pad and theroller surface; a separating pad holding member which holds theseparating pad therein and presses the separating pad against thefeeding roller; and a rolling member which abuts against the separatingpad free from the abutting state with the roller surface; wherein theseparating pad holding member holds a sliding member having a frictioncoefficient smaller than that of the separating pad in a region, againstwhich the roller surface abuts, and upstream of the separating pad in asheet conveyance direction, and the roller surface abuts against thesliding member and the separating pad in this order via the sheet duringthe rotation of the feeding roller.
 9. The sheet feeding deviceaccording to claim 8, wherein a boundary between the separating pad andthe separating pad holding member is formed more upstream in a sheetconveyance direction than a boundary between the separating pad and thesliding member, against which the roller surface of the feeding rollerabuts.
 10. The sheet feeding device according to claim 9, wherein therolling members are disposed on both sides at the roller surface of thefeeding roller in a sheet widthwise direction perpendicular to the sheetconveyance direction, and further, the boundaries between the separatingpad and the separating pad holding member are formed on both sides ofthe boundary between the separating pad and the sliding member whoseboundary has a width smaller than a distance between the rollingmembers.
 11. An image forming apparatus comprising: a recording unitwhich records an image on a sheet to be recorded; and a sheet feedingdevice which feeds the sheet toward the recording unit; the sheetfeeding device including: a feeding roller having a roller surface, onwhich a sheet is fed, at a part in a rotational direction; a separatingpad which is disposed opposite to the feeding roller and the sheets areseparated between the separating pad and the roller surface; aseparating pad holding member which holds the separating pad therein andpresses the separating pad against the feeding roller; and a rollingmember which abuts against the separating pad free from the abuttingstate with the roller surface; wherein the roller surface abuts againstthe separating pad holding member and the separating pad in this ordervia the sheet during the rotation of the feeding roller.
 12. The imageforming apparatus according to claim 11, wherein a friction coefficientof the surface of the separating pad holding member is smaller than thatof the surface of the separating pad.
 13. The image forming apparatusaccording to claim 11, wherein first and second regions, against whichthe roller surface of the feeding roller abuts, are set, and further,out of the boundary between the separating pad holding member and theseparating pad, a boundary of the second region is formed more upstreamin a sheet conveyance direction than a boundary of the first region. 14.The image forming apparatus according to claim 13, wherein the rollingmembers are disposed on both sides at the roller surface of the feedingroller in a sheet widthwise direction perpendicular to the sheetconveyance direction, and further, the second regions of the separatingpad holding member are disposed on both sides of the first region whoseboundary has a width smaller than a distance between the rollingmembers.
 15. An image forming apparatus comprising: a recording unitwhich records an image on a sheet to be recorded; and a sheet feedingdevice which feeds the sheet toward the recording unit; the sheetfeeding device including: a feeding roller having a roller surface, onwhich a sheet is fed, at a part in a rotational direction; a separatingpad which is disposed opposite to the feeding roller and the sheets areseparated between the separating pad and the roller surface; aseparating pad holding member which holds the separating pad therein andpresses the separating pad against the feeding roller; and a rollingmember which abuts against the separating pad free from the abuttingstate with the roller surface; wherein the separating pad holding memberholds a sliding member, which is made of a material harder than theseparating pad holding member, in a region, against which the rollersurface abuts, and upstream of the separating pad in a sheet conveyancedirection, and the roller surface abuts against the sliding member andthe separating pad in this order via the sheet during the rotation ofthe feeding roller.
 16. The image forming apparatus according to claim15, wherein a boundary between the separating pad and the separating padholding member is formed more upstream in a sheet conveyance directionthan a boundary between the separating pad and the sliding member,against which the roller surface of the feeding roller abuts.
 17. Theimage forming apparatus according to claim 16, wherein the rollingmembers are disposed on both sides at the roller surface of the feedingroller in a sheet widthwise direction perpendicular to the sheetconveyance direction, and further, the boundaries between the separatingpad and the separating pad holding member are formed on both sides ofthe boundary between the separating pad and the sliding member whoseboundary has a width smaller than a distance between the rollingmembers.
 18. An image forming apparatus comprising: a recording unitwhich records an image on a sheet to be recorded; and a sheet feedingdevice which feeds the sheet toward the recording unit; the sheetfeeding device including: a feeding roller having a roller surface, onwhich a sheet is fed, at a part in a rotational direction; a separatingpad which is disposed opposite to the feeding roller and the sheets areseparated between the separating pad and the roller surface; aseparating pad holding member which holds the separating pad therein andpresses the separating pad against the feeding roller; and a rollingmember which abuts against the separating pad free from the holdingstate in cooperation with the roller surface; wherein the separating padholding member holds a sliding member having a friction coefficientsmaller than that of the separating pad in a region, against which theroller surface abuts, and upstream of the separating pad in a sheetconveyance direction, and the roller surface abuts against the slidingmember and the separating pad in this order via the sheet during therotation of the feeding roller.
 19. The image forming apparatusaccording to claim 18, wherein a boundary between the separating pad andthe separating pad holding member is formed more upstream in a sheetconveyance direction than a boundary between the separating pad and thesliding member, against which the roller surface of the feeding rollerabuts.
 20. The image forming apparatus according to claim 19, whereinthe rolling members are disposed on both sides at the roller surface ofthe feeding roller in a sheet widthwise direction perpendicular to thesheet conveyance direction, and further, the boundaries between theseparating pad and the separating pad holding member are formed on bothsides of the boundary between the separating pad and the sliding memberwhose boundary has a width smaller than a distance between the rollingmembers.